page_title: Magnetic field
hierarchical_section_title: Magnetic field
caption_attribution_description: English: Photo of magnetic field of a horseshoe magnet. The magnetic field was made visible by sprinkling a layer of iron filings on a sheet of paper laid on top of the magnet. The filings are shaped like tiny needles, and orient themselves with their long axis parallel to the magnetic field at each point. The field pattern is slightly unsymmetrical, showing the magnet's righthand pole is slightly stronger than its left. Alterations to image: Converted to greyscale, increased brightness of high value pixels to eliminate background tint, cropped image rectangular, rotated image 90° CW, used clone tool to replace box with initials 'F. E. A.' in lower left corner.
context_page_description: A magnetic field is a vector field that describes the magnetic influence on an electric charge of other moving charges or magnetized materials. A charge that is moving in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. The effects of magnetic fields are commonly seen in permanent magnets, which pull on magnetic materials such as iron, and attract or repel other magnets, creating a torque. In addition, a magnetic field that varies with location will exert a force on a range of non-magnetic materials by affecting the motion of their outer atomic electrons. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, they are described as a map assigning a vector to each point of space or, more precisely—because of the way the magnetic field transforms under mirror reflection—as a field of pseudovectors.
  In electromagnetics, the term "magnetic field" is used for two distinct but closely related vector fields denoted by the symbols B and H.
context_section_description: A magnetic field is a vector field that describes the magnetic influence on an electric charge of other moving charges or magnetized materials. A charge that is moving in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field.  The effects of magnetic fields are commonly seen in permanent magnets, which pull on magnetic materials such as iron, and attract or repel other magnets, creating a torque.  In addition, a magnetic field that varies with location will exert a force on a range of non-magnetic materials by affecting the motion of their outer atomic electrons. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time.  Since both strength and direction of a magnetic field may vary with location, they are described as a map assigning a vector to each point of space or, more precisely—because of the way the magnetic field transforms under mirror reflection—as a field of pseudovectors.
  In electromagnetics, the term "magnetic field" is used for two distinct but closely related vector fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter (A/m). B, magnetic flux density, is measured in tesla (in SI base units: kilogram per second² per ampere), which is equivalent to newton per meter per ampere. H and B differ in how they account for magnetization. In a vacuum,the two fields are related through the vacuum permeability, ; but in a magnetized material, the terms differ by the material's magnetization at each point.
  Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated and are both components of the electromagnetic force, one of the four fundamental forces of nature.
  Magnetic fields are used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is conceptualized and investigated as magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass.
caption: The shape of the magnetic field produced by a horseshoe magnet is revealed by the orientation of iron filings sprinkled on a piece of paper above the magnet.
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